Method for the desulfurization of a steel melt

ABSTRACT

A steel melt is desulfurized in a ladle lined with dolomite magnesite or other refractory lining have an aluminum oxide content in excess of 70 percent (wt), by injecting at least 2,000 mm below the melt surface, finely divided calcium-containing compound after a basic-slag layer is applied to the surface of the deoxidized steel melt. The melt is held at a temperature of at least 1,530*C during desulfurization.



1. A METHOD OF DESULFURIZING A DEOXIDIZED STEEL MELT COMPRISING THE STEPS OF: COVERING THE DEOXIDIZED STEEL MELT WITH A BASIC-SLAG LAYER CONTAINING AT MOST 4 PERCENT BY WEIGHT FEO INTRODUCING AT A LOCATION AT LEAST 2,000 MM BELOW THE SURFACE OF THE DEOXIDIZED STEEL MELT COVERED WITH SAID BASIC SLAG LAYER A STREAM OF A CALCIUM-CONTAINING SUBSTANCE IN FINELY DIVIDED FORM IN A NUETRAL CARRIER GAS; MAINTAINING THE TEMPERATURE OF SAID MELT DURING THE INTRODUCTION OF SAID CALCIUM-CONTAINING SUBSTANCE THERETO AT AT LEAST 1,530*C, MAINTAINING SAID MOLTEN STEEL IN CONTACT WITH A LINING CONTAINING AT LEAST 70 PERCENT BY WEIGHT ALUMINIUM OXIDE DURING INTRODUCTION OF THE CALCIUM-CONTAINING SUBSTANCE THERETO; AND THE INTRODUCTION OF SAID CALCIUM-CONTAINING SUBSTANCE IS CARRIED OUT SO THAT SAID STEEL MELT CONTAINS AT LEAST 0.015 PERCENT BY WEIGHT ALUMINIUM.
 2. The method defined in claim 1 wherein said basic-slag layer has an FeO content in excess of 2 percent, further comprising controlling the introduction of the calcium-containing substance to reduce the FeO content of the basic slag layer to less than 2 percent by weight.
 3. The method defined in claim 1 wherein said gas is argon.
 4. The method defined in claim 3 wherein said calcium-containing substance is introduced into said melt by a lance extending downwardly through the melt.
 5. The method defined in claim 1 wherein said basic slag layer has essentially the following composition: 45 to 75 percent by weight calcium oxide, 0 to 25 percent by weight calcium fluoride, 0 to 20 percent by weight aluminum oxide, 0 to 30 percent by weight silicon oxide, 0.1 to 4 percent by weight FeO, and 0 to 10 percent by weight manganese oxide and/or phosphorus pentoxide and/or magnesium oxide.
 6. The method defined in claim 5 wherein said slag has approximately the following composition: 50 percent by weight calcium oxide, 20 percent by weight calcium fluoride, 12 percent by weight aluminum oxide, 10 percent by weight silicon oxide, 0.5 percent by weight FeO, the balance being manganese oxide, phosphorus pentoxide and magnesium oxide.
 7. The method defined in claim 5 wherein said calcium-containing substance is added to said melt in an amount corresponding to substantially 1.2 to 1.5 kg of calcium per ton of molten steel.
 8. The method defined in claim 7 wherein said calcium-containing substance is selected from the group which consists of elemental calcium, a calcium-silicon, intermetallic compound or alloy, and calcium carbide.
 9. The method defined in claim 8 wherein said calcium-containing substance is a calcium ferrosilicon containing substantially 30 percent by weight calcium, 60 percent by weight silicone and 10 percent by weight iron, the calcium ferro silicone being introduced into said melt in an amount of substantially 4 to 5 kgs per ton of molten steel.
 10. The method defined in claim 8 wherein said molten steel contains at least 0.015 percent by weight of the deoxidizing agent for said melt.
 11. The method defined in claim 1 wherein said slag layer is present in an amount of substantially 1 to 15 kgs per ton of molten steel. 